1. Field of the Invention
The present invention relates to a hinge device for use in a portable apparatus such as a lap-top or portable personal computer and more particularly to a hinge device having a mechanism for stopping a movable member of the apparatus at an open position, by virtue of the frictional force exerted by a spring member.
2. Description of the Related Art
U.S Pat. No. 4,571,456 discloses a portable personal computer which comprises a rectangular case, a keyboard attached to the case, and a display unit attached to the case by a hinge.
Connected by the hinge to the case, the display unit can rotate between a position (hereinafter referred to as "closed position") where it covers the keyboard and a position (hereinafter referred to as "opened position") where it stands upright at the rear of the keyboard. The hinge includes a mechanism which exerts a frictional force to stop the display unit at any position between the closed position and the open position.
A hinge having such a mechanism and designed to connect a display unit to the case of a personal computer is disclosed in Published Unexamined Japanese Patent Application No. 59-99111. This hinge comprises a shaft and a coil spring wound around the shaft. The shaft is fastened at one end to the display unit and at the other end to the case. As the display unit is rotated upward, the coil spring is wound more and more tightly around the shaft, whereby a frictional force is generated between the shaft and the coil spring. By virtue of this force, the display unit is held up at a position where the user takes his or her hand off the display unit, provided that the hinge shaft and the coil spring have a proper outside diameter and an appropriate inside diameter, respectively, and are set at correct positions. It requires much time and labor to make the shaft and the spring with sufficient precision and to set them in a correct positional relationship. consequently, the manufacturing cost of the hinge is inevitably high.